EP4418816A1 - Method for operating a continuous flow heater, continuous flow heater and computer program - Google Patents

Abstract

Method for operating a continuous flow heater (1) designed for operation on a three-phase power network (15), comprising at least the following steps: a) starting up the continuous flow heater (1), b) carrying out a voltage measurement to identify voltage differences with respect to the three phases (17, 18, 19), c) initiating the heating operation of the continuous flow heater (1) if the voltage difference determined in step b) is below a predetermined limit value. Furthermore, a continuous flow heater (1), a control device (4) and a computer program are proposed.

Description

The invention relates to a method for operating a continuous flow heater, a continuous flow heater and a computer program.

Instantaneous water heaters usually have a heating device with a heating coil or at least one heating rod, which converts electrical current into heat energy and transfers it to the water to be heated. Instantaneous water heaters in particular can achieve a high output of more than 15 kW [kilowatts]. Such an instantaneous water heater is used, for example, in the EP 3 702 694 A1 and in the EN 35 46 214 A1 described.

Heating coils/heating rods that are operated with alternating current [AC] can be used here. Due to the high electrical output, instantaneous water heaters are often operated with a three-phase connection, also known as three-phase current. In general, asymmetrical loads can occur in a three-phase power network, which are often triggered by single-phase consumers in the network. Current instantaneous water heaters always modulate the TRIACs with the same patterns on the individual phases. These asymmetrical loads on the three-phase power network can lead to an unbalanced load in the power network, which in turn can lead to heating of power plant components, particularly transformers and generators, which is accompanied by a reduction in energy efficiency and can even cause damage to the power plant components.

In addition, adverse effects on the electromagnetic compatibility (EMC) of the devices can occur because flicker and harmonics can occur, which make the use of costly EMC filters necessary.

Electric instantaneous water heaters typically have outputs between 18 kW and 27 kW. This results in currents between 26 A [amperes] and 39 A in a 3-phase network (400 V [volts]).

In a new installation, the cables and fuses are designed according to the current output of the instantaneous water heater. The cables are designed in such a way that the voltage drops by less than 3% at maximum load

In existing systems, the electric instantaneous water heater is usually designed to fit the existing building installation (fuse protection, cable cross-section). However, this is often difficult because the electrical cables run in the wall and you can only see the ends of the cables. In addition, there is often no information about whether the cables have been extended, re-laid, repaired, etc. In addition, you cannot see the condition of the cables in the wall. This means that the cables to the electric instantaneous water heater may be undersized. This can lead to a risk of placing more strain on the cables than desired/allowed when the electric instantaneous water heater is in operation.

Based on this, it is the object of the invention to propose a method for operating a continuous flow heater, a continuous flow heater and a computer program that at least partially overcomes the problems of the prior art described. In particular, the method and the continuous flow heater should enable measures with which an asymmetrical network load or unbalanced load (particularly due to unexpected or different cable conditions) can be detected as early as possible and, if necessary, avoided as far as possible or even compensated.

These objects are achieved by the features of the independent claims. Further advantageous embodiments of the solution proposed here are specified in the independent claims. It is pointed out that the features listed in the dependent claims can be combined with one another in any technologically expedient manner and define further embodiments of the invention. In addition, the features specified in the claims are specified and explained in more detail in the description, with further preferred embodiments of the invention being presented.

1. a) Inbetriebnehmen des Durchlauferhitzers,
2. b) Durchführen einer Spannungsmessung zur Identifikation von Spannungsdifferenzen bezüglich der drei Phasen,
3. c) Initiieren des Heizbetriebs des Durchlauferhitzers, wenn die in Schritt b) gemessene Spannungsdifferenz unterhalb eines vorgegebenen Grenzwertes liegt.

This is achieved by a method for operating a continuous flow heater which is designed to operate on a three-phase power grid and which method comprises at least the following steps:

1. a) Commissioning of the instantaneous water heater,
2. b) Carrying out a voltage measurement to identify voltage differences between the three phases,
3. c) Initiating the heating operation of the instantaneous water heater if the voltage difference measured in step b) is below a predetermined limit value.

The instantaneous water heater can have an inlet for cold water, a heating block, an outlet for hot water and a control and regulation device. Cold water can be fed to the instantaneous water heater via the cold water inlet, which is heated in the heating block, regulated or controlled by the control and regulation device and fed to the outlet for hot water for withdrawal. Knowing the flow rate of the water to be heated, water, the temperature of the cold water supplied and the target outlet temperature, the electrical power required to heat up to the target outlet temperature can be determined and controlled. A temperature sensor can also be arranged in the hot water outlet, which can enable (additional) control of a target outlet temperature.

The instantaneous water heater can be set up for operation on a three-phase power network. In particular, the instantaneous water heater can have a symmetrical connection of the three phases, whereby the phases can be switched using power electronic components, for example TRIACs. In particular, a star connection or a delta connection can be used here . The star connection is particularly preferred due to the lower mechanical effort involved in the connection.

The resistance-based heating element can in particular be a heating coil or a heating rod or a plurality of these, designed to convert electrical current into thermal energy in order to deliver this to a mass flow of the water to be heated. The heating element can generally be brought into direct contact with the water to be heated, which enables short reaction times of the heating device to be achieved. Heating wires, for example, are known for this purpose.

The resistance-based heating element consists at least partially of an electrically conductive material, whereby a large number of such materials are known, for example metal alloys such as nickel-copper alloys, chromium steels or nickel-chromium alloys are frequently used. In the context of these embodiments, a heating element can refer to a single heating element or a large number of redundant heating elements.

The instantaneous water heater can be put into operation according to step a). The commissioning can be initiated in particular by opening a tapping point (water tap) that is connected to a hot water outlet of the instantaneous water heater. A flow sensor can detect the mass flow of water flowing through the instantaneous water heater and transmit it to a control and regulation device of the instantaneous water heater. The control and regulation device can now supply the heating elements or the heating block with electrical energy, for example by controlling TRIACs, so that water heated to a target temperature can be drawn from the hot water outlet.

According to step b), at least one voltage measurement is carried out to identify voltage differences with respect to the three phases of the power grid. It is possible, for example, that the voltage difference between at least two phases or even with respect to all phases (to each other) is measured. It is also possible that in step a) a voltage is applied to the instantaneous water heater or that this is set so that it is lower than in heating mode. At least one of the voltage measurements can take place in the so-called "standby mode" of the instantaneous water heater. A "start-up mode" can also be provided in which an electrical voltage is applied to the instantaneous water heater or that this is set so that it is higher than in "standby mode" but lower than in heating mode. It is possible to carry out the voltage measurement individually for the phases and/or for at least two or even all three phases together.

The measured values of the voltage or the voltage difference can be stored and/or processed. In particular, differences and/or comparisons can be carried out automatically. It is possible for the instantaneous water heater to interact with a computing unit and/or a data storage device in order to carry out an evaluation of the measured or calculated voltage difference (based on measured voltage values). In this case, fixed or variable limit values can be read in, called up and/or processed, which are specified by the user, for example.

According to step c), the heating operation of the instantaneous water heater is initiated (only) when the voltage difference determined in step b) is below a specified limit value. Thus, the quality of the three-phase power grid is checked (at least once) before the heating operation starts, in particular directly by the connected instantaneous water heater.

It is preferred that the steps are carried out in the order specified here at least once (e.g. after retrofitting or initial installation) of a new instantaneous water heater. It is possible that this method is carried out each time the instantaneous water heater is (subsequently) started. It is possible that step b) and/or step c) are carried out more frequently than step a). It is possible that steps a), b) and/or c) are carried out at least temporarily in an overlapping manner. It is possible that step b) is carried out with a predetermined and/or variable repetition frequency, in particular with regard to further start-up processes and/or a longer-lasting step c). It is therefore particularly possible that after a first execution of step b), this is repeated several times, while step c) and/or this does not have to be carried out each time the subsequent step a).

It is possible that the heating operation of the instantaneous water heater is blocked if the voltage difference determined in step b) is above a specified limit value. In this case, a blocking and/or shutdown of the instantaneous water heater can be set up, whereby in the first case "only" the heating operation function can be deactivated and in the latter case the instantaneous water heater can be transferred to an "emergency stop" state. The extent to which the functionality of the instantaneous water heater is (temporarily) deactivated can be determined in relation to the extent to which the specified limit value of the voltage difference is exceeded and/or its extent over the number of phases.

An (electrical) output of the heating operation of the instantaneous water heater can be limited or reduced if the voltage difference determined in step b) is within a specified tolerance range. The fixed or variable tolerance range can depend on or be predetermined by the user and/or the device of the instantaneous water heater. The extent to which the functionality of the instantaneous water heater is limited can be determined in relation to the extent to which the specified limit value of the voltage difference is exceeded and/or its extent over the number of phases. In particular, it is possible that several, possibly adjacent sub-tolerance ranges are provided, which can result in different limitations. The electrical output is limited in particular so that the voltage drop and thus the power loss on the lines remains within a specified specification.

The (electrical) power can be limited for each phase, for example only for one or each of the three phases, for two phases and/or for all three phases. The limitations can also be monitored or communicated if necessary.

It is possible that step b) is also carried out in or during step c). During heating, the voltage can therefore continue to be measured continuously and/or intermittently (at the same time). If a voltage difference before heating and the voltage during heating (ΔU = U _standby - U _operation ) is too large, a predetermined action can be carried out.

A measurement result from step b) and/or a (mechanical or electronic) setting of the heating operation according to step c) can be displayed. It is of course also possible that not a measured value itself but a measurement symbol derived from it is displayed, for example an evaluative measurement symbol such as a green lamp for " voltage difference OK" and a red lamp for "voltage difference is clearly above the If a functionality of the instantaneous water heater is blocked, deactivated or restricted, this can also be made available to the user and/or operator on site and/or remotely via a network using a suitable display device .

Information about the phase quality can (also) be output based on step b). The homogeneity or the extent of the determined voltage difference can allow direct conclusions to be drawn about the quality of the cables in the walls of the buildings. Therefore, information about failure and/or overload risks, maintenance or repair requirements or the like can be communicated, again either on site and/or via a network.

1. i. Wenn eine Anzeige vorhanden ist, kann eine Meldung angezeigt werden, dass die (jeweilige(n)) Leitung(en) überlastet sind/werden.
2. ii. Man begrenz die elektrische Leistung, damit der Spannungsabfall (ΔU) und somit die Verlustleistung auf den Leitungen innerhalb einer vorgegebenen Spezifikation bleibt.
3. iii. Wenn der Spannungsabfall zu groß ist, kann der Elektro-Durchlauferhitzer abgeschaltet werden.
4. iv. Wenn eine Anzeige vorhanden ist und wenn der Spannungsabfall nur auf einer Leitung zu groß ist (z.B. nur der Leitung L2), wird eine Meldung angezeigt, dass ein Problem mit einer Leitung, nämlich L2, besteht
5. v. Wenn der Spannungsabfall nur auf einer Leitung zu groß ist (z.B. nur L2), wird nur bei dieser Leitung die (elektrische) Leistung begrenzt.

In particular, the following actions can be triggered (automatically) if a voltage difference that is too large is detected:

1. i. If an indicator is present, a message may be displayed indicating that the line(s) are/are becoming overloaded.
2. ii. Limit the electrical power so that the voltage drop (ΔU) and thus the power loss on the lines remains within a given specification.
3. iii. If the voltage drop is too large, the electric water heater may be switched off.
4. iv. If an indication is present and if the voltage drop is too large on only one line (eg only line L2), a message will be displayed that there is a problem with one line, namely L2
5. v. If the voltage drop is too large on only one line (e.g. only L2), the (electrical) power is limited only on this line.

In addition, a (current) load on each phase can be recorded based on the electrical voltage present at each phase. For example, the The electrical voltage present in each phase can be measured. Deviations in the voltages of the individual phases can indicate an unbalanced load.

It is also possible for the instantaneous water heater to be operated in such a way that phases in which a voltage difference that is too great was determined in step b) are subjected to a lower load or no load at all. In other words, at least one phase in which an increased load was determined during the implementation of step b) can be subjected to a lower load in a targeted manner. It is understood that in order to reach the target temperature for the heated water, the other phases or at least one other phase may have to be subjected to a higher load. If the load on the instantaneous water heater is less than 100% (of the nominal load, maximum load capacity), the phase in which an increased load was determined in step b) can be subjected to a correspondingly lower load, with the other two phases being subjected to a correspondingly higher load. In other words, the three phases can be subjected to an asymmetrical load, with the phase in which a lower load was determined in step b) being subjected to a lower load. In order to ensure that the target outlet temperature is reached, the phase identified as loaded in step b) can be loaded to such an extent that, with a load of 100% of the other two phases, the power required to reach the target outlet temperature can be achieved.

For example, if the instantaneous water heater requires 50% of its power, a phase identified as being loaded can be left unloaded and the other two phases can be loaded at 75% each. Alternatively, the phase identified as being loaded in step b) can be loaded at 30% and the other two at 60% each. The load distribution can be determined in particular with a view to avoiding flicker and/or achieving the desired target outlet temperature.
In some three-phase connections, the power consumption of two phases is always the same, whereas (only) the third phase can be modulated. The two phases with same power consumption can be operated at nominal power when carrying out step c) and the third phase (determined to be loaded in step b) can be operated at reduced (modulated) power, in particular by means of pulse width modulation (PWM). For such a connection, the following table shows various adjustable powers of the three phases P1, P2, P3 depending on a total power P _total (corresponding to the target outlet temperature) and a resulting maximum achievable power difference ΔP: P _Total [%] P1 [%] P2 [%] P3 [%] ΔP [%] 100.0 100.0 100.0 100.0 0.0 90.0 100.0 100.0 70.0 30.0 80.0 100.0 100.0 40.0 60.0 70.0 100.0 100.0 10.0 90.0 66.7 100.0 100.0 0.0 100.0 60.0 90.0 90.0 0.0 100.0 50.0 75.0 75.0 0.0 100.0 40.0 60.0 60.0 0.0 100.0 30.0 45.0 45.0 0.0 100.0 20.0 30.0 30.0 0.0 100.0 10.0 15.0 15.0 0.0 100.0

According to a further aspect, a control device for a continuous flow heater is also proposed, set up to carry out a method proposed here. The control device can for example have a processor and/or have one. In this context, the processor can for example carry out the method stored in a memory (of the control device). The control device can for this purpose be electrically connected in particular to a flow sensor, the heating block or the heating elements, a cold water temperature sensor and/or in the hot water outlet.

According to a further aspect, a continuous flow heater is proposed, designed for operation on a three-phase power network and comprising means for carrying out a method proposed here. The continuous flow heater can in particular have a flow sensor for detecting the mass or volume flow of water flowing through, a temperature sensor for detecting a cold water temperature and/or an outlet temperature of the water from the hot water outlet, a heating block or one or more heating elements and a regulating and control device.

According to a further aspect, a computer program is also proposed which is set up to (at least partially) carry out a method presented here. In other words, this relates in particular to a computer program (product) comprising commands which, when the program is executed by a computer, cause the computer to carry out a method proposed here. The computer program can in particular be executed on a control and regulating device of the instantaneous water heater.

According to a further aspect, a machine-readable storage medium is also proposed on which the computer program is stored. The machine-readable storage medium is usually a computer-readable data storage device.

The details, features and configurations discussed in connection with the method can also occur in the control device, the instantaneous water heater and/or the computer program proposed here and vice versa. In this respect, reference is made in full to the explanations there for a more detailed characterization of the features.

Here, a method for operating a continuous flow heater, a continuous flow heater and a computer program are provided which at least partially solve the problems described with reference to the prior art. In particular, the Process, the instantaneous water heater, the control and regulation device and the computer program reduce or even eliminate network loads such as an asymmetrical phase load and also compensate for an unbalanced load in the power grid, whereby any flicker that occurs can be limited or even reduced within a permissible range.

• Fig. 1: einen hier vorgeschlagenen Durchlauferhitzer, und,
• Fig. 2: ein Schaltbild eines hier vorgeschlagenen Durchlauferhitzers in einem dreiphasigen Stromnetz.

The invention and the technical environment are explained in more detail below with reference to the attached figures. It should be noted that the invention is not intended to be limited by the exemplary embodiments given. In particular, unless explicitly stated otherwise, it is also possible to extract partial aspects of the facts explained in the figures and combine them with other components and findings from the present description. In particular, it should be noted that the figures and in particular the size relationships shown are only schematic. They show:

• Fig.1 : a water heater suggested here, and,
• Fig.2 : a circuit diagram of a proposed instantaneous water heater in a three-phase power network.

Fig.1 shows an example and schematically a flow heater 1 proposed here. Water to be heated is fed into the flow heater 1 through a cold water inlet 2 and a flow sensor 3 can detect its mass flow and a temperature sensor 11 can detect a temperature of the cold water flowing into the cold water inlet 2, whereby the detected signals can be transmitted to the regulating and control device 4. The heated water can be taken from the flow heater 1 from a hot water outlet 8. The regulating and control device 4 can be connected to a switching unit 12, which can be set up to control and switch the voltage of the three phases of a mains connection 10 for supplying energy to the flow heater 1.

The control and regulating device 4 can also be connected to a control unit 9, on which a user can set various operating parameters, for example the target outlet temperature to which the instantaneous water heater 1 heats the water.

The control and regulation device 4 can also be connected to a motor-controlled valve 7, which can reduce the water flow through the instantaneous water heater 1 (infinitely). In this way, a reduction in the water flow can ensure that a target outlet temperature is reached. The instantaneous water heater 1 also has heating elements 6, which can be arranged in a heating block 5. The heating elements 6 can have a large number of resistance heating wires (heating wires).

Fig. 2 shows, by way of example and schematically, a circuit diagram of a flow heater 1 proposed here in a three-phase power network 15. The power network 15 can have a transformer 13, in particular a low-voltage transformer 13, which transforms high voltage from a high-voltage line for the power network 15 and has an earthing 14. The power network 15 can be three-phase and have a first phase 17, a second phase 18 and a third phase 19, each with a line and a PEN (protective earth neutral) line 20. For example, a single-phase consumer 16 connected to the power network 15 can place an uneven load on the phases 17, 18, 19, i.e. an unbalanced load can arise. In the present case, the single-phase consumer 16 is connected to the second phase 18. It is possible to use a voltage measuring device to determine the current voltage with respect to each of the phases, either in relation to one another and/or under different performance conditions of the flow heater 1.

After commissioning according to step a), the instantaneous water heater 1 can carry out a voltage measurement to identify voltage differences with respect to the three phases 17, 18, 19 (step b)) and finally initiate the heating operation of the instantaneous water heater 1, limit and/or block depending on how the voltage difference determined in step b) behaves with respect to a predetermined limit value.

As a precaution, it should be noted that the numerals used here ("first", "second", ...) primarily serve (only) to distinguish between several similar objects, sizes or processes, and in particular do not necessarily specify a dependency and/or sequence of these objects, sizes or processes. If a dependency and/or sequence is required, this is explicitly stated here or it is obvious to the person skilled in the art when studying the specifically described design. If a component can occur multiple times ("at least one"), the description of one of these components can apply equally to all or part of the majority of these components, but this is not mandatory.

List of reference symbols

1

Instantaneous water heater

2

Cold water inlet

3

Flow sensor

4

Control and regulation device

5

Heating block

6

Heating elements

7

motor-controlled valve

8

Hot water outlet

9

Control panel

10

Mains connection

11

Temperature sensor

12

Switching unit

13

transformer

14

Grounding power grid

15

Power grid

16

single-phase consumer

17

first phase

18

second phase

19

third phase

20

PEN cable

Claims (10)

Method for operating a continuous flow heater (1) designed to operate on a three-phase power network (15), comprising at least the following steps: a) Commissioning of the instantaneous water heater (1), b) Carrying out a voltage measurement to identify voltage differences between the three phases (17, 18, 19), c) initiating the heating operation of the instantaneous water heater (1) when the voltage difference determined in step b) is below a predetermined limit value. Method according to claim 1, wherein a heating operation of the continuous-flow heater (1) is blocked if the voltage difference determined in step b) is above a predetermined limit value. Method according to claim 1 or 2, wherein a power of the heating operation of the continuous-flow heater (1) is limited if the voltage difference determined in step b) is within a predetermined tolerance range. Method according to claim 3, wherein the power is limited in a phase-discrete manner. Method according to one of the preceding claims, wherein step b) is also carried out in step c). Method according to one of the preceding claims, wherein at least one measurement result from step b) or a setting of the heating operation according to step c) is displayed. Method according to one of the preceding claims, wherein information about the phase quality is output on the basis of step b). Regulating and control device (4) of a continuous flow heater (1), designed to carry out a method according to one of claims 1 to 7. Instantaneous water heater (1), designed for operation on a three-phase power network (15) and comprising a regulating and control device (4) and means for carrying out a method according to one of claims 1 to 7. Computer program comprising instructions which cause a continuous flow heater (1) according to claim 9 to carry out a method according to one of claims 1 to 7.

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